The average price for 1,000 fake followers is $18, according to one study by Barracuda Labs. Mr. Stroppa and Mr. De Micheli said some sellers bragged that they made $2 and $30 per fake account. A conservative estimate, they said, was that fake Twitter followers offered potential for a $40 million to $360 million business.

... The most coveted fake accounts tweet (or retweet) constantly, have profile pictures and complete bios, and some even link to Web sites that they claim belong to them. But in many cases, a close look reveals that some of the accounts were set up purely to retweet material from specific sites.

Twitter has sued five companies that create and sell fake accounts. The Times also reported that tech news site The Next Web created a piece of software that made it easier for otherwise inactive accounts to auto-tweet its stories. (Here's one.) TNW CEO Zee Kane said the company discontinued the project several months ago because it didn't add quality traffic.

The worst part: Jim Prosser, a spokesman for Twitter, says that about 40 percent of all Twitter users look like fake accounts because they only follow people and never tweet themselves. (Prosser's mom, for instance).

Also, people are allowed to sign up for multiple Twitter accounts and use them for different purposes, he says. Twitter, in other words, can't do a great deal about clever fakes: “It’s a hard problem,” Prosser told the Times.